It is known that the maximum power output of a combustion turbine is achieved by heating the gas flowing through the combustion section to as high a temperature as is feasible. The hot gas, however, heats the various turbine components, such as the combustor, transition ducts, vanes and ring segments, which it passes when flowing through the turbine. One aspect limiting the ability to increase the combustion firing temperature is the ability of the turbine components to withstand increased temperatures. Consequently, various cooling methods have been developed to cool turbine hot parts.
In the case of cooling of ring segments, ring segments typically may include an impingement plate welded to the ring segment and defining a plenum between the impingement plate and the ring segment. The impingement plate may include holes for passage of cooling air into the plenum. It has been noted that welding produces the potential for the impingement plate to crack as a result of the welding altering the material properties of the impingement plate. In addition, it has been observed that in the case of ring segments comprising thick panels defining a portion of a hot gas path through the turbine, the cooling provided by the impingement plate may not provide adequate cooling to the thick panel. In addition, further cooling structure, such as elongated passages that may be machined in the ring segment panel, may experience heating of cooling air channeled through the panel, with the result that portions of the panel do not receive adequate cooling.